The use of polyethylene to form packaging materials is generally known. For example, polyethylene may be extruded to form films, or it may be fabricated into articles via molding techniques, e.g. injection molding. Examples of articles that may be manufactured by injection molding processes are containers, for food storage or non-food storage. Such food storage containers may, for example, be used for storage and packaging of ice cream and yogurt. Such containers should be of relatively uniform thickness and should have a surface that is acceptable to the consumer. Small containers tend to be of lower wall thickness than larger containers, as less flow of polymer is required during the injection molding process in order to fill the mold. Furthermore, such containers should have acceptable total energy absorbed on impact at very low temperatures, and to further have low brittleness temperatures.
U.S. Pat. No. 6,136,924 discloses a composition containing ethylene polymers comprising a polymer of melt index MI2 of 5 to 1000 g/10 min and a polymer of melt index MI5 of 0.01 to 2 g/10 min, the ratio of these indices being from 500 to 50,000 and the weight ratio of the two polymers being equal to (30 to 70):(70 to 30).
U.S. Pat. No. 6,407,185 discloses a process for the preparation of a composition containing ethylene polymers comprising a polymer of melt index MI2 of 5 to 1000 g/10 min and a polymer of melt index MI5 of 0.01 to 2 g/10 min, the ratio of these indices being from 500 to 50,000 and the weight ratio of the two polymers being equal to (30 to 70):(70 to 30), according to which part of the ethylene, a catalyst derived from a transition metal having an intrinsic molecular weight distribution defined by an intrinsic Mw/Mn ratio less than or equal to 10 and a deactivation constant less than or equal to 0.5 h−1, and a cocatalyst are introduced into a first reactor, polymerization of the ethylene is carried out therein, a mixture comprising one of the polymers, the catalyst and the cocatalyst is drawn off from this reactor and the mixture and another part of the ethylene are introduced into a second reactor, which ethylene is polymerized to form the other polymer.
U.S. Pat. No. 4,192,935 discloses an ethylene polymer having a density in the range of about 0.940-0.960, a melt index in the range 100-200 and a ratio of weight-average molecular weight to number-average molecular weight of less than 5. The polymer is a copolymer of ethylene and at least one α-olefin having 4-10 carbon atoms e.g. butene-1, hexene-1 or octene-1. The preferred polymer is a copolymer of ethylene and butene-1. The polymers may be used in the injection molding of thin-wall containers, e.g. containers having a wall thickness of less than 0.7 mm, especially a thickness of less than 0.5 mm, and in particular a thickness of less than 0.4 mm.
U.S. Pat. No. 4,294,794 discloses a process for producing an ethylene polymer having a density in the range of about 0.940-0.960, a melt index in the range 100-200 and a ratio of weight-average molecular weight to number-average molecular weight of less than 5.
U.S. Pat. No. 5,015,511 discloses improved injection-molded LLDPE articles. Improved injection-molded LLDPE articles have a wall thickness in the range of about 0.15 mm to as much as 1.5 mm, and they are prepared using an LLDPE containing a sufficient amount of at least one C5-C12 1-alkene copolymerized with the ethylene to provide a density in the range of 0.91 to 0.945 g/cc, a melt flow rate in the range of 60 to 200 g/10 minutes, and an I10/I2 ratio of 7.2 to about 18.
U.S. Pat. No. 6,806,338 discloses an LLDPE produced using a single site catalyst, e.g., an LLDPE produced using a metallocene (m-LLDPE), which is preferably used in injection molding of food packaging material, especially closures for food containers exhibiting low levels of migration particularly suitable for use in packaging foods having a high fat content, typically less than 40 mg/dm2, e.g., less than 5 mg/dm2.
U.S. Patent Application Publication No. 2003/0105198 A1 discloses a polyethylene based composition comprising 0.05 to 0.5 wt. % of at least a saturated fatty acid amide containing 8 to 30 carbon atoms, 0 to 0.1 wt. % of an auxiliary lubricant selected among fatty acids, fatty acid esters, fatty acid salts, monounsaturated fatty acid amides, polyols containing at least 4 carbon atoms, monoalcohol or polyalcohol monoethers, glycerol esters, paraffins, polysiloxanes, fluorinated polymers and mixtures thereof, and 0 to 5 wt. % of one or more additives selected among the antioxidants, anti-acids, anti-UV stabilizers, coloring agents and antistatic agents.
U.S. Patent Application Publication No. 2003/0181608 A1 discloses the use of an LLDPE produced using a single site catalyst, e.g. an LLDPE produced using a metallocene (m-LLDPE), in injection molding of food packaging material, especially closures for food containers. Such materials have been found to exhibit low levels of migration, typically less than 40 mg/dm2, e.g. less than 5 mg/dm2, and are particularly suitable for use in packaging foods having a high fat content.
European Patent Application No. EP 1 357 136 A1 discloses single layer articles having improved dimensional stability produced by injection molding and consisting essentially of high-density polyethylene resins prepared with a bis-indenyl metallocene catalyst system.
International Publication No. WO 2005/014680 A1 discloses the use of a multimodal polyethylene composition as comonomers to ethylene at least two C4-12 alpha-olefins in injection molding.
Despite the research efforts in developing polyethylene compositions suitable for injection molding, there is a still a need for a polyethylene composition having improved properties suitable for injection molding. Additionally, there is still a need for a process for producing a polyethylene composition having improved properties suitable for injection molding.